Flame-resistant regenerated cellulose film



madam its normal state the film is extremely inflammable.

FLAME-RESISTANT REGENERATED CELLULOSE FILM William M. Weeding, Springdale, Cnn., Benedict F.

Melucci, Yonkers, N. Y., and Clemmon Porter, Stamford, C0nn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine N0 Drawing. Application July 25, 1955, Serial No. 524,306

6 Claims. (Cl. 117-137 The present invention relates to non-fibrous regenerated cellulose film of decreased infiammability and to methods for the manufacture thereof. More particularly the invention relates to clear transparent film containing diammonium phosphate and dicyandiamide in admixture as fire-retardants, crystallization of the fireretardant mixture being inhibited by the presence of a 1 water-soluble polyhydric alcohol in said film.

Non-fibrous regenerated cellulose film (both in its normal water-clear and in tinted forms) has long been a material of choice for imparting decorative effects to merchandising exhibitions represented by department store windows, store counters and show cases. Its use for this purpose has been hampered by the fact that in The amount of film used for this purpose is comparatively small, and no doubt for this reason regenerated cellulose film is not commercially available in fire-retardant form. A demand has therefore existed for a liquid which can be prepared and applied by the ultimate user of the film so as to render the film fire-retardant. Such liquid (to have practical use) should have the following properties:

1. It should be free from volatile solvents and be otherwise safe to use. i

2. It should be composed of readily-available materials, require only mixing by stirring, and be storagestable.

3. It should have a neutral or alkaline pH so as to avoid acid attack of the film.

4. It should leave no crystalline residue in the film so that the film when dry at normal temperature and hu midity retains its original clear and sparkling appearance.

5. It should introduce no color into the film, stiffen or embrittle the film unduly, give the film an odor, or render the film toxic.

In the past it has been proposed to use diammonium phosphate as fireproofing agent for non-fibrous regenerated cellulose film. It has been found, however, that when this salt is applied in the normal way (by impregnating the film with an aqueous solution of the salt and then drying the film) the salt precipitates as a crystalline deposit rendering the film unsuitable for use for decorative purposes; cf. U. S. Patent No. 2,262,634 to Cobbs (November 11, 1941).

The discovery has now been made that regenerated cellulose film can be made satisfactorily fire-retardant without formation of crystalline deposits therein by impregnating the film with an aqueous solution containing a polyhydric alcohol and a fire-retardant mixture in controlled proportions and drying the film, so as to deposit in the film an amount of the fire-retardant mixture equal to between about and 40% of the dry weight of the film and sufficient of the polyhydric alcohol (in range between about 5% and 20% ot' the dry weight of the film) 2 /z% to by weight of a water-soluble polyhydric altire-a cohol and about 2 /2% to 20% by weight of a mixture of 10 parts byweigliFof diammonium phosphate and 5 to f l0'parts by weight of dicyandiami'de as fire-retardants.

The solution employed meets the specification s set forth 0 calculating weights and proportions.

The dry film is defined as containing between 5% and 40%, based on its weight, of the mixture of fire-retardant agents referred to above and between about 2 /2% and 20% of a polyhydric alcohol, the amount of polyhydric alcohol being in addition sutficient to inhibit crystallization of the fire-retardant mixture in the film when in equilibrium with atmosphere at 73 F. and 50% relative humidity.

Dicyandiamide is present in the bath because it markedly increases the fire-retardant effect imparted by the diammonium phosphate. While the invention is not limited to any particular theory, it is possible that the polyhydric alcohol may enter into close association with the diammonium phosphate-dicyandiamide mixture, so as to render the mixture deliquescent or apparently more soluble than would otherwise be the case.

The bath is readily prepared by dissolving the materials together with stirring, heat being applied as necessary to effect complete solution, after which the liquid may be cooled to room temperature. The baths have a pH of about 7.

The film is treated simply by immersion in the solution. The amount of polyhydric alcohol and solids picked up is a function both of the composition of the bath and the length of time the film remains therein. The film picks up about 200% of its weight of the solution when it is allowed to remain therein until saturated, and in commercial practice the speed of the film through the solution is generally controlled so that its liquid pickup is about of its dry weight. The film may be dried at room temperature as no chemical reaction is involved.

The solution should contain at least about 2 /2% by weight of the fire-retardant mixture, this being about the least required to give noticeable fire-retardant properties even when the film is immersed until it is completely saturated. On the other hand, it is difficult to form solutions containing excessively large amounts of the fireretardant mixture and 20% is therefore set as the upper practical limit. Very satisfactory results have been obtained when the solution contains between about 5% and 10% by weight of the mixture.

As a rule of thumb, considering glycerolv as the polyhydric alcohol, the solution should contain at least about 2% by weight when the solution contains the minimum effective amount of fire-retardant mixture. This is about the least which will prevent crystallization and film embrittlement. At the other extreme, we have not found it necessary for the bath to contain more than 10% by weight of the alcohol, and indeed a larger amount tends to cause blocking when the film is rolled.

The minimum effective amount of polyhydric alcohol in each case will depend on the particular alcohol selected, the ratio of dicyandiamide to diammonium phosphate, and the temperature and relative humidity at which the dried film is used. A suitable amount, however, is readily arrived at by marking a series of simple laboratory tests. Any water-soluble polyhydric alcohol may be used, such as glycerol, ethyleneglycol, mannitol, and sorbitol, and the lower polyglycols. Glycerol is preferred for the reasons that this alcohol is readily commercially available and has given very satisfactory results.

of the solution by the ultimate consumer.

Maximum fire-retardation takes place when the weight ratio of diammonium phosphate to the dicyandiamide is about 10:7, and the invention includes compositions approaching this optimum within the weight ratio of 10:5 and 10: 10.

The film on entering the solution described may be in wet swollen condition. The solution may thus be employed during regenerated cellulose film manufacture. It is a particular advantage of the invention, however, that the film may be in dry condition, thus permitting use The bath may contain such dyes and perfume as are commonly used by decorators, including fluorescent dyes. These materials are not features of the invention.

The invention will be more particularly described b reference to the examples which follow. These examples represent embodiments of the invention and are not to be construed as limitations thereon.

Example 1 A combined plasticizing-fireproofing bath was prepared as follows. 10 grams of diammonium phosphate and 7.1 grams of dicyandiamide were dissolved in 325 grams of hot 8% aquoeus glycerol. The solution thus prepared contained 5% by weight of the fire-retardant mixture and 7.6% by weight of glycerol, the remainder being water. The pH of this bath was neutral to litmus.

Example 2 A similar solution was prepared as follows:

grams of diammonium phosphate and 7.1 grams of dicyandiamide were dissolved in 154 grams of hot 8% aqueous glycerol. The resulting solution contained 10% by weight of the fire-retardant mixture and 7.2% of glycerol.

Example 3 The foregoing solutions were tested as fire-retardants for regenerated cellulose film as follows:

A sheet of dry unlacquered commercial non-fibrous regenerated cellulose film was immersed for five minutes in the solution of Example 1, a second sheet was similarly immersed in the solution of Example 2, and a third sheet (the control sheet) was similarly immersed in an 8% aqueous glycerol solution. All three sheets were removed, excess liquid wiped off, and dried in frames by storage for 24 hours in a normal atmosphere of 50% relative humidity and 73 F. At the end of this time the color, appearance, drape, feel and odor of all three sheets were compared and found practically identical. The sheets were clear and sparkling and no crystalline deposits were observed.

Several strips 2" x 5" were cut from each of the sheets and tested for combustibility by the method wherein the strips are mounted vertically resting on one of their long sides and the flame of a cigarette lighter is applied to the middle of the upper edge and the presence or absence of self-supporting combustion noted. Results are as follows:

Solution Results Example 1 No self-sustainhig flame. Example 2 No self-sustaining flame. The induced flame extinguished on removal of the llghter more abruptly than the flame of Example 1. Control Film burned rapidly and completely with selfsustaining flame.

, in said film an amount of fire-retarding mixture equal to between about 4% and of the dry weight of said film and sufficient polyhydric alcohol in range between 5% and 20% of the dry weight of said film to inhibit crystallization of said mixture in said film when dry.

2. A process according to claim 1 wherein the polyhydric alcohol is glycerol.

3. A process according to claim 2 wherein the weight ratio of the diammonium phosphate to the dicyandiamide is about 10:7.

4. Non-fibrous regenerated cellulose film having deposited therein between about 4% and 40% of its dry weight of a mixture of diammonium phosphate and (heyandiamide as fire-retarding agents, the weight ratio of said diammonium phosphate to said dicyandiamide being between about 10:5 and 10:10, and sutficient of a polyhydric alcohol, in range between about 4% and 20% of the dry weight of the film, to inhibit crystallization of said fire-retardant mixture therein.

5. Film according to claim 4 wherein a polyhydric alcohol is glycerol.

6. Film according to claim 5 wherein the ratio of diammonium phosphate to dicyandiamide is about 10:7.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR TREATING NON-FIBROUS REGENERATED CELLULOSE FILM, WHICH CONSISTS ESSENTIALLY IN IMPREGNATING SAID FILM WITH AN AQUEOUS SOLUTION CONTAINING ABOUT 2% TO 10% BY WEIGHT OF A WATER-SOLUBLE POLYHYDRIC ALCOHOL PLASTICIZER THEREFOR AND 2 1/2% TO 20% BY WEIGHT OF A MIXTURE OF DIAMMONIUM PHOSPHATE AND DICYANDIAMIDE IN WEIGHT RATIO BETWEEN ABOUT 10.5 AND 10.10 AS FIRERETARDING AGENTS AND DRYING SAID FILM, THEREBY DEPOSITING IN SAID FILM AN AMOUNT OF FIRE-RETARDING MIXTURE EQUAL TO BETWEEN ABOUT 4% AND 40% OF THE DRY WEIGHT OF SAID FILM AND SUFFICIENT POLYHYDRIC ALCOHOL IN RANGE BETWEEN 5% AND 20% OF THE DRY WEIGHT OF SAID FILM TO INHIBIT CRYSTALLIZATION OF SAID MIXTURE IN SAID FILM WHEN DRY. 